6lo Working Group D. Dujovne
Internet-Draft Universidad Diego Portales
Intended status: Informational M. Richardson
Expires: October 26, 2018 Sandelman Software Works
April 24, 2018
IEEE802.15.4 Informational Element encapsulation of 6tisch Join and
Enrollment Information
draft-richardson-6tisch-enrollment-enhanced-beacon-01
Abstract
In TSCH mode of IEEE802.15.4, as described by [RFC8180],
opportunities for broadcasts are limited to specific times and
specific channels. Nodes in a TSCH network typically frequently send
Enhanced Beacon (EB) frames to announce the presence of the network.
This document provides a mechanism by which small details critical
for new nodes (pledges) and long sleeping nodes may be carried within
the Enhanced Beacon.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Layer-2 Synchronization . . . . . . . . . . . . . . . . . 3
1.3. Layer-3 synchronization IPv6 Router solicitations and
advertisements . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Definition . . . . . . . . . . . . . . . . . . . . . 4
2.1. Protocol Example . . . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Change history . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[RFC7554] describes the use of the time-slotted channel hopping
(TSCH) mode of [ieee802154]. As further details in [RFC8180], an
Enhanced Beacon is transmitted during a slot designated a broadcast
slot.
EDNOTE: Explain why broadcasts are rare, and why we need them. What
the Enhanced Beacon is, and what Information Elements are, and how
the IETF has a subtype for that area. Explain what kind of things
could be placed in Information Elements, how big they could be, and
how they could be compressed.
1.1. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
[RFC2119] and indicate requirement levels for compliant STuPiD
implementations.
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1.2. Layer-2 Synchronization
As explained in section 6 of [RFC8180], the Enhanced Beacon has a
number of purposes: synchronization of ASN and Join Metric, timeslot
template identifier, the channel hopping sequence identifier, TSCH
SlotFrame and Link IE.
The Enhanced Beacon (EB) is used by nodes already part of a TSCH
network to annouce its existance. Receiving an EB allows a Joining
Node (pledge) to learn about the network and synchronize to it. The
EB may also be used as a means for a node already part of the network
to re-synchronize [RFC7554].
There are a limited number of timeslots designated as a broadcast
slot by each router. These slots are rare, and with 10ms slots, with
a slot-frame length of 100, there may be only 1 slot/s for the
beacon.
1.3. Layer-3 synchronization IPv6 Router solicitations and
advertisements
At layer 3, [RFC2461] defines a mechanism by which nodes learn about
routers by listening for multicasted Router Advertisements (RA). If
no RA is heard within a set time, then a Router Solicitation (RS) may
be multicast, to which an RA will be received, usually unicast.
Although [RFC6775] reduces the amount of multicast necessary to do
address resolution via Neighbor Solicitation messages, it still
requires multicast of either RAs or RS. This is an expensive
operation for two reasons: there are few multicast timeslots for
unsolicited RAs; if a pledge node does not hear an RA, and decides to
send a RS (consuming a broadcast aloha slot with unencrypted
traffic), many unicast RS may be sent in response.
This is a particularly acute issue for the join process for the
following reasons:
1. use of a multicast slot by even a non-malicious unauthenticated
node for a Router Solicitation may overwhelm that time slot.
2. it may require many seconds of on-time before a new pledge hears
a Router Soliciation that it can use.
3. a new pledge may listen to many Enhanced Beacons before it can
pick an appropriate network and/or closest Join Assistant to
attach to. If it must listen for a RS as well as find the
Enhanced Beacon, then the process may take a very long time.
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2. Protocol Definition
[RFC8137] creates a registry for new IETF IE subtypes. This document
allocates a new subtype TBD-XXX.
This document documents a new IE subtype structure is as follows. As
explained in [RFC8137] the length of the Sub-Type Content can be
calculated from the container, so no length information is necessary.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD-XXX |R|P| res | proxy prio | rank priority |
+-+-+-+-+-+-+-+-+-+-------------+-------------+-----------------+
| pan priority | |
+---------------+ +
| Join Proxy lower-64 |
+ (present if P=1) +
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+ +
| network ID |
+ variable length, up to 16 bytes +
~ ~
+ +
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+
proxy priority the proxy prority value contains a number from 0 to
0x7f. Lower numbers are considered to be a higher preference. A
priority of 0x7f indicates that the announcer should never be
considered as a viable enrollment proxy. Lower value indicates
willing to act as a Join Proxy as described in
[I-D.ietf-6tisch-minimal-security]. Only unenrolled pledges look
at this value.
pan priority the pan priority is a value set by the DODAG root to
indicate the relative priority of this LLN compared to those with
different PANIDs. This value may be used as part of the
enrollment priority, but typically is used by devices which have
already enrolled, and need to determine which PAN to pick.
Unenrolled pledges MAY consider this value when selecting a PAN to
join. Enrolled devices MAY consider this value when looking for
an eligible parent device.
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rank priority the rank "priority" is set by the 6LR which sent the
beacon and is an indication of how willing this 6LR is to serve as
an RPL parent within a particular network ID. This is a local
value to be determined in other work. It might be calculated from
RPL rank, and it may include some modifications based upon current
number of children, or number of neighbor cache entries available.
This value MUST be ignored by pledges, it is for enrolled devices
only.
R the Router Advertisement flag is set if the sending node will act
as a Router for host-only nodes that need addressing via unicast
Router Solicitation messages.
P if the Proxy Address bit is set, then the lower 64-bits of the
Join Proxy's Link Layer address follows the network ID. If the
Proxy Address bit is not set, then the Link Layer address of the
Join Proxy is identical to the Layer-2 8-byte address used to
originate this enhanced beacon. In either case, the layer-2
address of any IPv6 traffic to the originator of this beacon may
use the layer-2 address which was used to originate the beacon.
join-proxy lower-64 if the P bit is set, then 64 bits (8 bytes) of
address are present. The Link Layer address of the Join Proxy is
fe80 (as for any Link Layer address), and the bits given in this
field.
network ID this is an variable length field, up to 16-bytes in size
that uniquely identifies this network, potentially among many
networks that are operating in the same frequencies in overlapping
physical space. The length of this field can be calculated as
being whatever is left in the Information Element.
In a 6tisch network, where RPL is used as the mesh routing protocol,
the network ID can be constructed from a SHA256 hash of the prefix
(/64) of the network. That is just a suggestion for a default value.
In some LLNs where multiple PANIDs may lead to the same management
device (the JRC), then a common value that is the same across all
PANs MUST be configured.
2.1. Protocol Example
Here will be three examples of processing.
3. Security Considerations
All of the contents of this Information Element are sent in the
clear. The containing Enhanced Beacon is not encrypted.
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The Enhanced Beagon is authenticated at the layer-2 level using
802.15.4 mechanisms using the network-wide keying material. Nodes
which are enrolled will have the network-wide keying material and can
validate the beacon.
Pledges which have not yet enrolled are unable to authenticate the
beacons.
4. Privacy Considerations
The use of a network ID may reveal information about the network.
The use of a SHA256 hash of the DODAGID, rather than using the
DODAGID directly provides some cover the addresses used within the
network. The DODAGID is usually the IPv6 address of the root of the
RPL mesh.
An interloper with a radio sniffer would be able to use the network
ID to map out the extend of the mesh network.
5. IANA Considerations
Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID.
This entry should be called 6tisch-Join-Info.
6. Acknowledgements
Thomas Watteyne provided extensive editorial comments on the
document.
7. References
7.1. Normative References
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work
in progress), November 2017.
[I-D.ietf-6tisch-minimal-security]
Vucinic, M., Simon, J., Pister, K., and M. Richardson,
"Minimal Security Framework for 6TiSCH", draft-ietf-
6tisch-minimal-security-05 (work in progress), March 2018.
[ieee802154]
IEEE Standard, ., "802.15.4-2015 - IEEE Standard for Low-
Rate Wireless Personal Area Networks (WPANs)", 2015,
.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
DOI 10.17487/RFC2461, December 1998,
.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
.
[RFC8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information
Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May
2017, .
7.2. Informative References
[I-D.ietf-6tisch-dtsecurity-secure-join]
Richardson, M., "6tisch Secure Join protocol", draft-ietf-
6tisch-dtsecurity-secure-join-01 (work in progress),
February 2017.
[RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180,
May 2017, .
Appendix A. Change history
The rank priority was expanded to 2 bytes.
00: The extension was originally for the use of Pledges only during
the enrollment/join process. Additional information was desired for
nodes which have already enrolled in order to aid in the joining
(selecting of a parent) of an RPL DAG. The term "join" was realized
to be ambiguous, meaning different things to different groups, and so
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the activity where the pledge finds a "Join Proxy" has been named
"enrollment"
-1: This is an evolution of an earlier proposal which provided for
storing an entire IPv6 Router Adverisement in an Informational
Element. It was deemed too general a solution, possibly subject to
mis-use. This proposal restricts the use to just the key pieces of
information required.
Authors' Addresses
Diego Dujovne (editor)
Universidad Diego Portales
Escuela de Informatica y Telecomunicaciones, Av. Ejercito 441
Santiago, Region Metropolitana
Chile
Phone: +56 (2) 676-8121
Email: diego.dujovne@mail.udp.cl
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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